This invention relates generally to fluid flow meters and more particularly to meters which translate the proportionate travel of an object within the meter housing which is biased against the direction of flow of the fluid being measured.
A simple and inexpensive meter of this type is comprised of a bullet-nosed object held against the fluid flow by a compression spring which is centrally supported within a housing. The downstream deflection of the object is calibrated and read through a window in the housing or transparent length of pipe. Although these devices have generally performed satisfactorily, for more accuracy a longer more precise spring is required, sometimes thus precluding their practicality where space is a factor. Also their inherent economy is compromised since the cost of springs which will perform adequately increases geometrically as they are lengthened.
More complex meters of this type such as that disclosed in U.S. Pat. No. 4,041,891, employ propellers which are biased against the direction of flow by torsion springs. However, in these devices the springs are typically located outside the housing in which the fluid is flowing, thus requiring special treatment to seal off a dry spring and indicator chamber and requiring other additional components in the form of seals, gears and various moving parts.
Other meters employ propellers by measuring their rotational speed and also must transfer readings externally by structures more complex than a window or transparent length of pipe. Some of these structures include routing the liquid out of its general path of flow so that the propeller can be normal thereto, use of a worm gear in order that the propeller can be normal to the general path of fluid flow, and counting electronic pulses transmitted through a non-conductive housing by ferromagnetic elements on the propeller. All of these latter types of rate of flow meters can be relatively accurate in a confined space, but also are complex devices requiring high initial cost and expensive maintenance.